1. Field of the Invention
This invention relates to a device to lay flat a film tube which is drawn from an inflated film bubble generated in a film blowing system. The device includes flat platens which delimit the film bubble and which are placed, in the form of a wedge, against the film bubble. The platens are positioned in front of the squeeze rollers of a film take-up and winding device and are provided with slip elements arranged transverse relative to the take-up device. A driven reversing frame, which holds the lay-flat platens, supports the squeeze rollers, and supports guide rollers and turning bars about its rotating axis in a pivoting fashion.
2. Description of Related Art
Lay-flat platens which are reversible up to 360.degree. and which have pivotable guide rollers and turning bars of this type are known, for example, from DE-OS 2,035,584, DE-PS 2,156,079, DE-PS 3,506,772 and DE-OS 4,303,952. The slip elements, which enable an improved sliding of a film tube over the lay-flat platens, can consist of strips having low friction surfaces or coatings, of rolls, or of small rollers.
In spite of the low-friction guiding of a film tube to be laid flat on lay-flat platens, problems may arise when laying a film tube flat due to the fact that the tube has a surface which is not yet fully cooled and, as a result, is sticky. Particular difficulties arise during the laying flat process when a reversing take-up is provided. A reversing take-up occurs when the squeeze rollers downstream of the lay-flat platens are driven so as to reverse by angles of up to 360.degree.. Difficulties also arise when the rollers are driven so as to turn continuously. For a reversing take-up, when laying flat very sticky film tubes, an undesired edge fold formation tends to occur in the top region of the lay-flat platens. This edge fold results from a twisting of the film tube due to the reversing turning movement. For a nonadhering film with good sliding properties, this twisting can be compensated for by a transversely oriented sliding movement of the film with respect to the lay-flat platens. However, for a highly adhesive and sticky film, this type of compensation is no longer possible since the film adheres too strongly to the slip elements, rolls, or small rollers. Undesirable edge fold formation results prior to the squeeze rollers.